[Update 2015-04] Beginning with 12c, dba_views has a column text_vc of varchar2(4000) that 
captures the (first 4000 bytes of) the view definition.


Q: How do I find which view's definition contains a given string?
A: Other than spooling dba_views.text to a file and read the file, you can build another table
   based on dba_views converting the text column to a CLOB type and query your table.
   In fact, you can use this method to search in trigger code (dba_triggers.trigger_body) or
   any LONG type column data. (But of course trigger_body is PL/SQL code and so can be easily 
   searched in dba_source.)

The following is run in an account with select_catalog_role in Oracle 10.2.0.4.

create table myviewtable (
owner       varchar2(30),
view_name   varchar2(30),
text        clob);

insert into myviewtable (owner, view_name, text)
select owner, view_name, to_lob(text) from dba_views;

Then you can query the CLOB field, case-insensitively if you want:

SQL> select owner, view_name from myviewtable where dbms_lob.instr(lower(text), 'histogram') > 0;

OWNER                          VIEW_NAME
------------------------------ ------------------------------
SYS                            V_$SQL_WORKAREA_HISTOGRAM
...

SQL> select max(length(text)) from myviewtable;

MAX(LENGTH(TEXT))
-----------------
            33270

SQL> select owner, view_name, length(text) from myviewtable where length(text) > 12000 order by 3;

OWNER                          VIEW_NAME                      LENGTH(TEXT)
------------------------------ ------------------------------ ------------
...
SYS                            ALL_IND_STATISTICS                    13163
...
SYS                            ALL_OBJECTS                           13885
...
SYS                            STRADDLING_TS_OBJECTS                 16214
...
SYS                            STRADDLING_RS_OBJECTS                 17214
...
CBFACT                         HLA_RCPT_LOOKUP_WITH_RAW_V            33270

If the views (that you care) had 4000 chars or less in its definition, you could use VARCHAR2 instead 
of CLOB for even easier search.

create table myviewtable2 (
owner       varchar2(30),
view_name   varchar2(30),
text        varchar2(4000));

insert into myviewtable2 select owner, view_name, substr(text,1,4000) from myviewtable;

In my case, that truncates long lines so that's bad:

SQL> select max(length(text)) from myviewtable2;

MAX(LENGTH(TEXT))
-----------------
             4000

If you really really don't like to create a table for this search, you can use function long2clob in 
the undocumented package dbms_metadata_util:

SQL> select obj#, sys.dbms_metadata_util.long2clob(1000000, 'SYS.VIEW$', 'TEXT', rowid) from sys.view$ where sys.dbms_metadata_util.long2clob(1000000, 'SYS.VIEW$', 'TEXT', rowid) like '%CAPTURE_MESSAGE_NUMBER%';

        OBJ# SYS.DBMS_METADATA_UTIL.LONG2CLOB(1000000,'SYS.VIEW$','TEXT',ROWID)
------------ ----------------------------------------------------------------------------------------------------
        8113 select "INST_ID","SID","SERIAL#","CAPTURE#","CAPTURE_NAME","LOGMINER_ID","STARTUP_TIME","STATE","TOT
             AL_PREFILTER_DISCARDED","TOTAL_PREFILTER_KEPT","TOTAL_PREFILTER_EVALUATIONS","TOTAL_MESSAGES_CAPTURE
             D","CAPTURE_TIME","CAPTURE_MESSAGE_NUMBER","CAPTURE_MESSAGE_CREATE_TIME","TOTAL_MESSAGES_CREATED","T
             OTAL_FULL_EVALUATIONS","TOTAL_MESSAGES_ENQUEUED","ENQUEUE_TIME","ENQUEUE_MESSAGE_NUMBER","ENQUEUE_ME
             SSAGE_CREATE_TIME","AVAILABLE_MESSAGE_NUMBER","AVAILABLE_MESSAGE_CREATE_TIME","ELAPSED_CAPTURE_TIME"
             ,"ELAPSED_RULE_TIME","ELAPSED_ENQUEUE_TIME","ELAPSED_LCR_TIME","ELAPSED_REDO_WAIT_TIME","ELAPSED_PAU
             SE_TIME","STATE_CHANGED_TIME" from gv$streams_capture

        8115 select "SID","SERIAL#","CAPTURE#","CAPTURE_NAME","LOGMINER_ID","STARTUP_TIME","STATE","TOTAL_PREFILT
             ER_DISCARDED","TOTAL_PREFILTER_KEPT","TOTAL_PREFILTER_EVALUATIONS","TOTAL_MESSAGES_CAPTURED","CAPTUR
             E_TIME","CAPTURE_MESSAGE_NUMBER","CAPTURE_MESSAGE_CREATE_TIME","TOTAL_MESSAGES_CREATED","TOTAL_FULL_
             EVALUATIONS","TOTAL_MESSAGES_ENQUEUED","ENQUEUE_TIME","ENQUEUE_MESSAGE_NUMBER","ENQUEUE_MESSAGE_CREA
             TE_TIME","AVAILABLE_MESSAGE_NUMBER","AVAILABLE_MESSAGE_CREATE_TIME","ELAPSED_CAPTURE_TIME","ELAPSED_
             RULE_TIME","ELAPSED_ENQUEUE_TIME","ELAPSED_LCR_TIME","ELAPSED_REDO_WAIT_TIME","ELAPSED_PAUSE_TIME","
             STATE_CHANGED_TIME" from v$streams_capture


SQL> select owner, object_name from dba_objects where object_id in (8113, 8115);

OWNER                          OBJECT_NAME
------------------------------ ------------------------------
SYS                            GV_$STREAMS_CAPTURE
SYS                            V_$STREAMS_CAPTURE

Dbms_metadata_util.long2clob only works on a few data dictionary tables for a few columns 
(limited by utl_xml it calls). If it doesn't work for you, set serveroutput on and run the 
query to see if there's any interesting error.